Friday, July 06, 2007
Should older pregnant moms get genes screened?
Most experts agree that the best time - biologically speaking - for a woman to get pregnant is when she's in her mid-20's, but today more women than ever are choosing to have children after age 35 and even 40. Given the news reports of some celebrities having babies later in life (actress Holly Hunter had twins at 47 and Jane Kaczmarek had her third child at 46), as well as the occasional report of grandmothers having babies, some women may think that having a baby later in life isn't a big deal.
The numbers bear it out: More women than ever over the age of 40 are having babies - more than 103,000 in 2004 - twice as many as in 1990, according to the U.S. Centers for Disease Control and Prevention.
But the reality is that having babies later in life can be more difficult and brings along increased risks for the mom-to-be and the baby.
However, modern medicine can help. In addition to in-vitro fertilization, or IVF, doctors have the technology to test embryos for genetic defects before they are implanted.
It's called "PGD" - preimplantation genetic diagnosis. When an embryo is divided into just eight cells, one cell is removed and tested for genetic defects.
This is used when parents may carry a gene for a genetic disorder such as Huntington's disease or sickle-cell disease. PGD could be recommended to parents of any age because they could pass the gene for these disorders to their child.
Older moms have older eggs. Dr. Dorothy Mitchell-Leef, a reproductive specialist in Atlanta told me, "Women in their 40's have a double set of problems: Their eggs are aging and they don't have as many as they used to have." As the eggs age, the chromosomes don't divide as well - which increases the risk of having three chromosomes or just one when there are supposed to be a pair.
So the same basic technique used in PGD can also be used for screening genetic defects that can lead to miscarriages or Down syndrome, which is the result of chromosome abnormalities. This is called PGD for aneuploidy screening.
A new study presented at the European Society of Human Reproduction and Embryology and published in the New England Journal of Medicine this week says using PGD for screening in older moms decreases their chance of carrying the baby to term. (Full Story).
Why the lower birth rate? The invasiveness of extracting a cell may be damaging the embryo, or reducing the overall genetic information in the embryo could be contributing to birth failures.
I spoke with several fertility experts who were not surprised at these results. But as Dr. Marcelle Cedars from the University of California, San Francisco put it, "Women above a certain age ask for it (the screening) and we spend a lot of time talking them out of it." Now doctors have a study to point to that confirms what they believed already: Screening embryos just because the mom is older doesn't increase her chance of having a healthy baby - as a matter of fact, it can decrease the chance.
While the experts I spoke with agreed with the study results, other reports say not all fertility experts agree with the findings. If you're in your late 30s or 40s and are trying to get pregnant (and don't have a family history of debilitating disorders), would you insist on screening your embryo before implantation?
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